Energy, exergy and economic analyses of a novel solar-lignite hybrid power generation process using lignite pre-drying

Abstract

Efficient utilization of lignite for power generation as well as development of solar-coal hybrid energy conversion systems are being aggressively researched currently. This paper proposed a novel solar-lignite hybrid power generation incorporating a lignite pre-drying, in which the solar energy collected from the flat plate collectors were beneficially utilised to drive the pre-drying process using air as the drying medium, upgrading the lignite caloric value, increasing the boiler heat flux and correspondingly boosting the electric power output. The models of energy, exergy and economics calculations for the proposed system were developed to assess the overall system thermal efficiencies as well as the net economic benefit. The graphical exergy analyses of the lignite combustion and solar-driven pre-drying processes were also performed. The net solar-to-electricity conversion efficiency as well as the cost of the solar generated electric power were computed to evaluate the solar utilization effectiveness. The results of the detailed thermodynamic and economic analyses showed that the proposed system can produce additional 29.6 MW net electric power with the overall energy and exergy efficiencies improvement of 0.5 and 1.6 percentage points, respectively, as 57.1 MW solar thermal energy is introduced. The cost of the solar generated electric power can be as low as $0.035/(kW·h) and the net annual benefits of the proposed system can reach $36.4 M, or even reach $95.7 M when the proposed system is considered as a carbon dioxide mitigation contributor.